Doctoral Dissertation Research: Social organization and decision-making in fission-fusion primate societies

University Of California-Davis, Davis CA

Investigators

Abstract

How do animals who live in social groups make decisions about what the group should do? Does a dominant individual lead the group, or can multiple individuals contribute to decision-making? This doctoral dissertation project will investigate group decision-making in wild spider monkeys, who frequently split into smaller groups and re-form the larger group (fission-fusion) when feeding. The investigator hypothesizes that fission-fusion social grouping is driven by the energetic needs of multiple individuals and promotes egalitarian social organization (equal power among individuals). How groups decide when and where to move in their habitat and who exerts the most influence is vital to identifying the costs and benefits of group living, and this research will provide insight into the emergence of egalitarian social dynamics in human societies. This project will support academic training and mentorship for students under-represented in STEM fields, thereby fostering interest in the sciences at the K-12 level and providing field research opportunities for undergraduate students. Additionally, this project will promote international collaborations, hands-on workshops, and public science seminars. A key challenge to studying how group decisions are made is determining the motivations driving individuals' decisions, and thus the link between individual needs and collective action. Some evidence suggests that fission-fusion social organization may promote egalitarian social norms by allowing individuals to split away from despotic group members when decisions about what to do or where to go do not align with their individual needs. Using wild black-handed spider monkeys as a model system, this study combines well-established observational field methods of behavior, foraging theory models, and laboratory techniques for quantifying energy balance, to provide a deeper mechanistic understanding of the collective decision-making process in fission-fusion societies. The investigator will collect observational data on leadership and decision-making and analytical data on individual energetic state as indicated by C-peptide analysis of non-invasively collected urine samples. The project will address three main hypotheses: 1) spider monkeys engage in shared decision-making, 2) groups tend to fission when conflicts between individuals are high, and 3) individuals lead according to their physiological need as opposed to dominance or social power.